Rotational coring systems employed by the oil and gas industry, the geothermal-energy industry, and the mining industry all employ a nonrotating inner core barrel/rotating outer core barrel configuration with a swivel bearing connection at the top of the dual-concentric core barrel, whereas kerf excavation is provided by either roller cone, roller wheel, or drag-type core-bit configurations. Because of the rotational kinetics associated with state-of-the-art core bits and because of internal wear, or internal gauge loss, torsional loads are often placed upon the emerging core, resulting in the fracture and rotation of the core by the core bit, ultimately, leading to core-jamming at the core catcher assembly, whereas natural fractures as well as core-bit induced fractures often result in wedge-jamming within the core barrel itself.
Small-diameter lightweight coring systems, particularly, the wire-line conveyed core-sampling apparatus employed by the mining industry, have a tendency while progressing downward through the rock to deviate considerably because of the inadvertent application of excessive weight upon the light-duty coring equipment. Consequently, deviation of the corehole trajectory from the vertical often becomes excessive, thus, necessitating costly remedial measures directed at reducing the corehole deviation to within acceptable limits.
Furthermore, if the down-hole coring apparatus is driven to the right, or clockwise, by a downhole motor, as viewed from above, the reactive torque transmitted from the face of the diamond-impregnated core bit (or any other high-friction drag-type cutting head) to the downhole motor, results in a corehole deviation pattern that spirals to the left, or counterclockwise, as portrayed by the trace of the corehole trajectory on a horizontal plane. In the parlance of the trade, this downhole lateral force is referred to as "left-hand torque", and the downhole motor is said to "crank to the left", whereas the course of the corehole is said to "walk to the left". In down-hole coring operations, particularly, those that must be performed with minimal corehole deviation, a coring system that prevents the inadvertent application of excessive amounts of weight upon the light-duty coring apparatus, a coring system that is capable of eliminating corehole deviation induced by reactive torque, and a coring system that is able to minimize geologically-induced corehole deviation, would be particularly desirable.